The present invention relates to anti-theft systems for motor vehicles, and particularly to a system which prevents the operation of the motor vehicles unless a coding device, such as a combination code keyboard, is properly operated.
A large number of diverse types of systems for preventing theft of motor vehicles have been devised, but the known systems generally are far from entirely satisfactory, which is evident from the fact that this problem of motor vehicles thefts has not diminished. Thus, one type of system includes mechanical locking devices, for example for locking the steering wheel or accelerator pedal; but such mechanical devices are inconvenient to use, time-consuming in applying and removing, and easily rendered ineffective by professional thieves having equipment for breaking or cutting the mechanical devices. Another type of theft-prevention system includes alarms which are actuated when an unauthorized attempt is made to penetrate the vehicle; such systems, however, usually suffer from a high rate of false alarms thereby diminishing their credibility when actuated, and also subjecting the owner to considerable inconvenience. A third type of anti-theft system includes electrical switches or similar devices located at a secret place known only to the authorized user which can be used for disabling the vehicle ignition system, the fuel supply, or the like, in order to prevent the operation of the vehicle; such secret switches, however, are easily circumvented by a professional thief by merely tracing the wires under the hood.
A still further type of anti-theft system includes a coding device, such as a keyboard, which allows the operator to input a code. The code is compared to a predetermined code stored within the system to control an enabling device which enables the starting and operation of the vehicle only when a match occurs. Examples of the latter type of anti-theft systems are described in U.S. Pat. Nos. 4,447,850, 4,438,426, 4,180,043, 4,090,089, 3,947,693, 3,788,422, 3,718,202, and 3,544,804.
An object of the present invention is to provide an anti-theft system for motor vehicles of the latter type but having advantages in a number of respects as will be described more particularly below.